feat: add default encoder for Pattern type

[PrettyWood]

Change Summary

As we allow Pattern to be used as a regular type and considering we now support Pattern when generating
schema (#1768) it makes sense to also add a default encoder for it

Related issue number

closes #2045

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)

[codecov]

Codecov Report

Merging #2056 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #2056   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         4094      4096    +2     
  Branches       821       822    +1     
=========================================
+ Hits          4094      4096    +2     

Impacted Files	Coverage Δ
pydantic/json.py	100.00% <100.00%> (ø)

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